1. Field of the Invention
The invention concerns a device for projecting a color image onto a screen, the device enabling color image recording and a color image reproduction with greater fidelity than possible with existing techniques. In an alternative embodiment, the device and the therewith employed process provides for full color stereoscopic image reproduction.
2. Description of the Related Art
In existing devices and processes for image recording in full color, the color information is detected by the separate recording of the respective spectral regions which correspond to the primary colors red, green and blue. In the subsequent image reproduction, the primary color partial pictures are combined into a full color image. A device of this type is known for example from WO WO98/49837.
Fundamentally, both in photochemical processes as well as in electronic processes, photoelectric transformers are involved in reproducing visual contents in color.
The length and the breadth of the mentioned spectral regions is largely dictated by the spectral sensitivity of the color receptors in the human eye. Typical values for both image recording as well as image reproduction lie in the wavelengths of
Each of these spectral regions can, via its color coordinates, be assigned a point on the standard color chart ((x,y)-chromaticity diagram) according to DIN 6164 (Mutze et al., ABC of Optics, published by Dausien, Hanau, 1972). The totality of all of these principle colors defined in this mannerxe2x80x94the primary valences (reference stimulus) (see U.S. Pat. No. 4,409,614, incorporated herein by reference)xe2x80x94form a triangle in the standard color chart, as shown in FIG. 1 (continuous line). By an additive color mixing of the basic colors, each color can be represented within this, triangle. Colors outside of this triangle cannot be represented. In particular, spectrally pure colors with their characteristic high color saturationxe2x80x94these lying on the outlying peripheral curve, the spectral color chart curvexe2x80x94are not reproducible.
One possibility for enlarging the representable color space is comprised in the selection of primary valences with narrower spectral ranges for image reproduction. In the extreme case the primary valences (primary colors) are finally spectrally pure and lie on the spectral color curve, as shown in FIG. 1 (dashed line). However the price for the thus achieved enlargement of the color space, for example in projection systems which use broad band emitting temperature radiators (bodies that deliver radiant heat, whose frequency (color) depends on the temperature, commonly used as wide-band strong sources of light) as projection lamps, is a substantial loss in image intensity. This becomes more distinct with the narrowing of the bandwidth of the base colors, since out of the entire emission spectrum only correspondingly small emission ranges are utilized.
If on the other hand one employs spectrally pure light sources, such as for example lasers, then this disadvantage does not occur. However, such systems are very complex and expensive. Besides this, the enlarging of the color space does not necessarily result in increased color reproduction fidelity. Rather, calculations must be made on the enlarged color reproduction side as well as on the recording side. Otherwise, there could result, false colors which must be corrected using suitable color transformers. The later however results again in a reduction in the size of the color space.
The invention is thus concerned with the task of providing a device for projection of a color image, which makes it possible not only to produce an enlarged color space, but rather also to reproduce it, wherein on the recording side the calculation is carried out relative to the reproduction side enlarged color space, wherein there is no substantial loss or penalty in image brightness, wherein the emitted light of the projection lamp is utilized in an efficient manner and wherein expensive spectrally pure light sources are not required.
It has been found that an alternative embodiment of the device can be employed for recording and reproducing three dimensional images. The device offers the advantage, that with few manipulative steps it is possible to alternate between the mode xe2x80x9cimage recording and reproducing with enhanced color reproduction faithfulnessxe2x80x9d and the mode xe2x80x9cthree dimensional recording and reproductionxe2x80x9d.
By the use of the device, a process for recording and reproducing color images is realized, in which during image recording of the recording object (target) two color images are recorded in parallel, wherein for the image reproduction a projection process is employed, wherein light from a single projection lamp is divided into multiple partial light bundles via a first dichroic mirror with triple band pass characteristic. The three transmission ranges B1, G1, R1 of the first dichroic mirror lie within the wavelength range for a dominant excitation of the blue, green and red receptors in the human eye. One of the transmitted partial light bundles is directed through a color image modulator, which contains the image information from the one recorded color image. Another mirrored partial light bundle is directed through a further color image modulator, which obtains the color image information from the other recorded color image. The two partial light bundles are, after their modulation, again reunited into one light bundle via a second dichroic mirror with triple band pass characteristic. The second dichroic mirror exhibits three transparent or transmissive ranges B2, G2 and R2, which are within the wavelength range for a dominant excitation of the blue, green and red receptors in the human eye and which lie outside the transmission ranges B1, G1, R1 of the first dichroic mirror. Beam recombination occurs in the manner, that the partial light bundle transmitted through the first dichroic mirror is reflected at the second dichroic mirror.
The two color images are recorded in such a manner, that light from the object being recorded is first split preferably by a dichroic mirror with three transmissive ranges B1, G1, R1. The transmitted partial light bundle serves for recording the one color image. The reflected partial light bundle serves for recording the other color image. The two color images are recorded by a stereo camera. The dichroic mirror with the transmission ranges B1, G1, R1 is preferably integrated in a beam splitter which is provided as an enclosed construction component in front of the lenses of the stereo camera. For image reproduction the observer preferably wears a pair of glasses, which have in front of one eye an interference filter with transmission ranges B1, G1, R1 and in front of the other eye an interference filter with the transmission ranges B2, G2, R2. Thereby the left eye exclusively receives the color image recorded with the left camera lens and the right eye exclusively color image recorded with the right camera lens, whereby a stereoscopic vision with a particularly good color fidelity and saturation is produced.